This page has vocabulary often on the TOEFL (which tends to mean the words are generally useful). The words are sorted by root (that is the word part that is most important to the meaning like "act" in "reaction" and by prefixes (a part that gets added on to the beginning of a word like "un" in "uncomfortable") and suffixes (the part added to the end of a word like "er" in "worker"). Please email or ask in class if the website is confusing. With any luck, you'll find it helpful.
2. scholar.google.com and books.google.com
These are two good resources for finding scholarly things in English. The first searches recent articles (and you may not be able to see all the article without paying, but you will likely be able to see at least an abstract); the second site searches books. You'll be able to see the entire book if it was published before 1923 but only parts of books published after then. (The date relates to American Copyright law.)
This website focuses on spelling. Look around to find tips for how to spell as well as games and exercises.